1. Field of the Invention
The present invention concerns a method and a device in order to control the workflow of an MR measurement (data acquisition), wherein multiple slices of a predetermined volume segment of an examination subject are excited and measured in each repetition of the MR measurement with continuous table feed, particularly in such a method and device wherein the MR signals are acquired with the SMS technique (“Sliding MultiSlice” technique).
2. Description of the Prior Art
The SMS technique is a special axial multislice measurement with continuous feed of a patient bed during an MR measurement. Measurements with table driven continuously through the magnets of the magnetic resonance system serve to expand the “field of view” (FOV) in the direction of the table displacement and can simultaneously limit the measurement area within the magnet. Concurrent with the continuous table feed is the acquisition of the expanded field of view in multiple stations given a stationary table. After all data of a station are acquired, the patient is moved with the patient bed to the next station and exposed to the measurement during the travel. Given axial multislice measurements with continuous table feed, the examination region or the volume within the patient from which images should be acquired is normally subdivided into multiple slice stacks. Given simple axial multislice measurements with continuous table feed, these slice stacks are acquired in succession. During the measurement of one of these slice stacks, the measurement position follows a fixed anatomical position within the examination subject driven with the table. The speed with which the table is continuously moved is selected such that the travel path during the acquisition time of a slice stack is, for example, equal to twice the length of a slice stack. It is thereby possible for corresponding slices of different slice stacks to be measured identically. Different slices of a slice stack or different slices of different slices stacks are measured differently, however. In particular, k-space lines of the slices that correspond to one another are measured (acquired) at different positions within the magnetic resonance system. This has the following disadvantage.
Since the B0 field of every real magnetic resonance system is not ideally homogeneous, and the gradient fields are not ideally linear, similar MR measurements at different positions lead to different distortions of the calculated images. After the composition of the images, this leads to discontinuities at the borders of the slice stacks since anatomically adjacent slices that are associated with different slice stacks occupy opposite positions within the respective slice stack. This problem is addressed and improved by the SMS technique, for example.
The SMS technique described by H.-P. Fautz and S. A. R. Kannengiesser in “Sliding Multislice (SMS): A New Technique for Minimum FOV Usage in Axial Continuously Moving Table Acquisitions”, Magnetic Resonance in Medicine 55:363-370 (2006) allows acquisition-dependent differences between different slices of a slice stack to be minimized in comparison to other acquisition techniques. However, specific requirements with regard to the number of slices of a slice stack and with regard to the user parameters defining a resolution of the achieved imaging must be satisfied in specific MR measurements in which multiple slices are acquired with continuous table feed (for example in the SMS technique).